how many square bales of hay does a horse eat in a month

Hi,
I am hoping of getting a quarter horse in about a year. I am trying to get an idea what the costs would be.
So i was wondering How many of those small Square bales of hay a quarter horse eats in a month(in winter).

P.S. Does a horse need hay in summer when it has almost 5 acres of good grass to eat???

In general, a horse will eat 2% of his weight in hay a day. So if you have a 1000lb horse, he will eat roughly 20lbs of hay. An average square bale (in my area) weighs 50lbs. so about 1/4 to 1/3 of a bale a day.

None of that takes into consideration the moisture of the hay, what type of hay it is, the age and condition of the horse... Talk to someone who is knowledgeable about the horse you are going to buy (preferably a trusted trainer) and go from there.